Transcript Time From the Perspective of a Particle Physicist

Supernova and Neutron Stars
For heavy white dwarves with a companion star
• acquire mass, if becomes > 1.4 M(Sun)
SUPERNOVA (Ia). p + e  n + neutrino
• Usually leaves neutron star
For high mass stars
• fusion continues beyond C,O to Iron
• if Mass(core) > 1.4 M(Sun) core collapses in
SUPERNOVA (II)
• leaves either Neutron Star or Black Hole
• Most SN are this type
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White Dwarves Mass vs Radius
S. Chandrashekar 1910-1995
worked out in 1930 on boat from
India to England prior to grad
school. Later became professor at
Chicago. Nobel prize 1983
Earth radius
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Supernovas and Core Collapse
• massive stars have fusion to heavier nuclei
(Neon, Silicon, Sulpher, etc)
• end up with core of Iron nuclei plus 26 unbound
“free” electrons for every Fe
• electrons are “degenerate” as so close together 
provide most of the pressure resisting gravity
• enormous stress. electrons “give way” leaves
“hole” size of Earth in center of star
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Supergiant  Iron Core
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During Supernova
core collapse gives 200 billion degrees  very high
energy photons
• breaks up many nuclei
Fe  26p + 31n O  8p + 8n
• new nuclei form  photons, n, and p strike shell around
core  see in SN debris
• p + e  n + neutrino (and nuclei decaying)
1. Burst of neutrinos. 1000 times more energy than from
light (photons)
2. Leftover neutron star
•
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Core Collapse
core collapses into
mostly neutrons –
very hot
outer layers rush into
“hole” smashing into
shock wave from core
Many nuclear
reactions  form
heavy elements
Core=30 km wide
Hole=13000 km wide
Type II expends
energy increasing size
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Supernova Explosions
1 billion times brighter
then the Sun for a few
months
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Supernova 1987a (in movie)
Large Magellanic
Cloud Type II
180,000 LY away
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Detection of neutrinos from SN1987A in Japan
and Ohio
SN produced 1058 neutrinos
1015 n/cm2 at Earth
1018 neutrinos from SN passed
through any person’s body
Traveled 175,000 light years to Earth
Passed through Earth
24 were detected in detectors made from 100
tons of water located in underground mines
in Ohio, Russia and Japan
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Nuclear Synthesis
•
All elements heavier than Helium are made inside
stars
up to Iron - fusion in Red Giants
heavier than Iron (and some lighter) - Supernova
explosions
• Stars lose matter at end of life-cycle
becoming Red Giants (can detect)
Supernova debris (can detect)
and this matter forms new stars (and planets and us)
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Supernova Debris SN1987a
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Supernova Debris
Crab Nebula M1
Cassiopeia A maybe
Supernova 1054 (observed by
observed in 1680
Chinese and Arabs). Has neutron
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NEUTRON STARS
In supernova explosion core collapses
• e- + p  n + n
• neutrons remain giving neutron “star” about
1% protons/electrons
• very hot (200 billion degrees) and very small
(10-30 km - DeKalb County)
• so very, very dense. 1 cm3  100 million tons
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White Dwarf
Neutron Star
Mass (relative to
Sun)
Radius
1.0 (always <
1.4)
5000 km
1.5 (always <
3)
10 km
Density
106 g/cm3
1014 g/cm3
Properties determined by “degenerate” electrons and neutrons.
neutron/electron mass ratio = 2000, neutron star much smaller and
denser
Senior level physics classes do the quantum mechanics which
predict radius versus mass
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Angular Momentum + Neutron Stars
Angular momentum = MASS x VELOCITY x RADIUS
decreasing RADIUS increases VELOCITY
Angular momentum is conserved:
spinning chair
ice skater
formation of neutron star in collapse of
larger spinning star
NEUTRON STARS II
• spin rapidly  from >100 Hz to less than 1 Hz
• EM radiation from protons/electrons + spin  large
magnetic fields
• observe as repeating flashes of light PULSARS and
seen in debris of known supernova explosions
• discovered in 1967 by grad student Jocelyn Bell. Her
advisor Anthony Hewitt won Nobel prize. Found in
Crab Nebula where Chinese had recorded a supernova
in 1054. First called LGM for “little green men”
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Crab Nebula
radio
infrared
visible
period = 30 Hz or
0.033 sec and can
be “seen” in visible
and X-ray
X-ray
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Rotating Neutron Star
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